This invention relates generally to hydraulic jacks, and more particularly concerns a valve for closely controlling the release of pressure within the hydraulic jack.
Hydraulic jacks such as those disclosed in U.S. Pat. Nos. 2,548,902 and 2,548,903 have met with great success in commercial marketplaces. They are compact, safe, relatively lightweight, and can lift heavy loads without excessive exertion by the jack user.
When the user of the disclosed or somewhat similar jacks wishes to lower a jack-elevated load, he operates a release valve. Commonly such a release valve includes a needle valve stem which can be screwed toward and away from a valve seat to correspondingly close or open the valve, and which consequently halts or permits jack-lowering fluid flow.
When the jack is extended and is supporting a heavy load, the fluid pressures experienced by this release valve can be high. Inattentive operation of the valve can result in the jack-supported load being lowered somewhat more rapidly than the jack user may anticipate. In other instances, it may be desireable to lower the supported load at a predetermined rate, or to halt the load-lowering action at a given point. Previously offered release valves have not been adapted to perform such operations precisely.
It is accordingly the general object of the present invention to provide a hydraulic jack having an improved release valve for jack lowering operations. More specifically, it is an object to provide a release valve which provides relatively precise control of the jack lowering operations.
Yet another object is to provide a jack having a precise release valve which is reliable and rugged in operation, and which provides relatively long service life.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.